The invention relates to improvements in methods of and in apparatus for making continuous streams of fibrous material, and more particularly to improvements in methods of and in apparatus for simultaneously producing two continuous streams of comminuted particles of tobacco and/or other smokable material.
It is already known to simultaneously make two continuous tobacco streams in a so-called twin cigarette rod making machine wherein each of the two streams is converted into the filler of a discrete cigarette rod. Each rod is then severed to yield a succession of plain cigarettes of unit length or multiple unit length. Similar procedure can be resorted to for simultaneous making of two continuous cigarillo, cigar or cheroot rods. Reference may be had, for example, to commonly owned U.S. Pat. No. 5,009,238 granted Apr. 23, 1991 for "Apparatus for supplying fibrous material to machines for simultaneously producing a plurality of cigarette rods" and to commonly owned U.S. Pat. No. 5,072,741 granted Dec. 17, 1991 for "Method of and apparatus for making plural tobacco filler streams". The disclosures of these patents are incorporated herein by reference. The patented apparatus employ means for dividing a relatively wide main flow of tobacco particles into two narrower flows each of which is directed against the underside of the lower reach of a foraminous belt conveyor to form thereon a stream which is then ready for trimming (involving removal of surplus tobacco particles) and conversion into a rod-like filler.
It is not only desirable but indeed necessary to ensure that the distribution of various types of tobacco particles in, as well as all other characteristics of, one of the streams match the characteristics of the other stream. This ensures that the quality of rod-shaped articles of the tobacco processing industry which are obtained as a result of subdivision of one of the cigarette rods matches the quality of articles which are obtained as a result of subdivision of the other cigarette rod. Such uniformity of characteristics of the two simultaneously produced tobacco streams can be achieved only by accurately controlling the treatment of tobacco particles in each and every part of a so-called distributor (also known as hopper) which serves to convert a mass of tobacco particles into the two narrower flows and to direct the narrower flows toward the foraminous conveyors in order to build two discrete tobacco streams. The distributor comprises a duct which is located immediately upstream of the foraminous conveyors and is intended to direct each of the two narrower flows toward the underside of the lower reach of the respective conveyor. As a rule, the duct defines a path for the upward flow of tobacco particles forming the two narrower flows. Such path is narrow, as measured transversely of the foraminous conveyors, but is rather wide in the direction of advancement of tobacco streams with the respective foraminous conveyors. This ensures the establishment of two relatively long stream building zones wherein successive increments of the two ascending narrower flows of tobacco particles are converted into successive increments of the respective streams. Tobacco particles of the two narrower flows which enter the lower end of the duct to ascend toward the respective foraminous conveyors exhibit the tendency to mingle, and this can affect the quality of the two streams in a sense that the composition of one of these streams deviates from the composition of the other stream. In fact, it has been observed that the rather thoroughly intermixed particles of each of the two narrower flows entering the duct tend to undergo a classification according to size and/or shape which adversely affects the quality of rod-like fillers of the two tobacco rods. Some classification of particles according to size and/or shape can take place within as well as at the inlet to the aforementioned duct. Any, even minute, classification within the duct will adversely affect the quality, such as the density, the so-called draw resistance, the weight and/or other important characteristics of the rod-shaped articles which are obtained from the two streams, namely which are obtained by trimming, densifying, draping and subdividing the streams downstream of the stream building stations.